1. Field of the Invention
The invention pertains to art of thermal cycling switches.
2. Description of the Prior Art
While the idea of providing a switch arrangement in which a switch knob must first be pushed before it can be rotated is considered to be known, special problems can arise in connection with incorporating a push-to-turn arrangement in a thermal cycling switch intended to control periods of time during which current flows through a cooking surface unit. This is so because of the movements effected by the bimetal assembly in such a switch are relatively small and the problem of getting accurate control at relatively low wattage input, such as at 5 percent, is especially difficult when some of the cooperating parts are of molded plastic. For example, the moding tolerances of these parts may be in the order of 0.002-0.003 inches (0.0508-0.0762mm) while a variation in movement of the adjustable spring arm relative to the bimetal assembly of 0.002-0.004 inches (0.0508-0.1016mm) may result in a variation of the desired 5 percent input of 2 to 12 percent. While the initial calibration of the switch can compensate for most of this variation in range, it is important that the parts when once calibrated will give the desired repeatability of a particular input thereafter. The problem of repeatability is basically only experienced at a low input, because at a higher inputs the setting of the switch itself by the user can compensate to obtain the desired input.
The desirability of having a push-to-turn arrangement for a thermal cycling switch used on cooking ranges is of course for purposes of safety. One aspect of the invention is the provision of an arrangement which is adapted to be incorporated in the standard thermal cycling switch of my assignee, as disclosed in U.S. Pat. No. 3,634,802, without a significant cost being incurred in tool changes and new piece costs.